<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>BFC</title>
    <style>
  *{
    margin: 0;
    padding: 0;
  }
  .box{
    width: 200px;
    height: 200px;
  background-color: lightblue;
  border: 1px solid #000;
  }
  .box1{
    margin-bottom: 50px;
  }
  .box2{
    margin-top:30PX;
  }
    </style>
</head>
<body>
    <div style="overflow:hidden;"></div>
    <div class="box box1">Box1</div>
    <div class="box box2" >Bpx2</div>
</body>
</html>